Question

Neon has 2 isotopes: one with atomic mass 20 amu and abundance of 90% and another with atomic mass 22 amu and10% abundance. What is the weighted average atomic mass of neon?

Answer 1

20.2 amu

Step-by-step explanation

To calculate the average atomic mass between two isotopes you need their mass and their abundance in the nature given in %, now you only do the math:

f1M1 + f2M2 = The average

20 * 0.9 + 22 * 0.1 = 20.2

f = the fraction of the natural abundance of the isotope (usually we have this number in %, so all you need to do is divide by 100 and use this value in the calculations)

M = the mass number or weight of the isotope